This web page provides supporting references for the report:
Risky Business: Invasive species management on National Forests
A review and summary of needed changes in current plans, policies and programs
(www.kettlerange.org/weeds/)
Return to the supporting references page by clicking here.

Biological Invasions of Alien Plants in the Interior Columbia River Basin

by George Wooten and Peter Morrison, Methow Research Station, Sierra Biodiversity Institute, February, 1995

(Excerpted from Key Elements for Ecological Planning: Management Principles, Recommendations, and Guidelines for Federal Lands East of the Cascade Crest in Oregon and Washington, a report to the Interior Columbia Basin Ecosystem Management Project, Cara Nelson, ed., Columbia River Bioregion Campaign, Science Working Group, 41 S. Palouse St., Walla Walla, WA 99362, May 19, 1995. The authors can be contacted at Pacific Biodiversity Institute, Winthrop, WA 98862, ph. 509-996-2490).

INTRODUCTION

Biological invasions of alien plants present one of the most serious threats to long-term maintenance of ecosystem health and biodiversity (Westman, 1990, Tyser and Key, 1988, Mack, 1986, 1981) in the interior Columbia River basin (ICRB). Invasion and colonization by alien plants reduces the health and integrity of ecosystems in many ways. These invasions degrade resource values (Bucher, 1984, Pimental, 1986), alter ecosystem processes (Walker and Vitousek, 1991, Verstraete and Schwartz, 1991, Melgoza et. al., 1990), affect trophic levels (Vitousek et. al., 1987, Kerpez and Smith, 1987, Harty, 1986), and can lead to endangerment and extinction of native species (Flather, 1994, Parenti and Guerrant, 1991). Interspecific interactions between native and introduced species adversely affect more than 50% of all threatened and endangered species in the United States (Flather, 1994). This is the second most important cause of species endangerment (after habitat loss). Given these impacts, prevention and control of alien plant invasions should be integral to ecosystem management policies in the ICRB.

In most cases, biological invasions occur gradually and inconspicuously. By the time that public awareness develops, the effects are often irreversible and resources may be irretrievably committed, productivity lowered and biodiversity reduced (USDI-BLM, 1994). Land management agencies have made some efforts to control a certain class of biological invaders (noxious weeds), but have never seriously addressed the causes of biological invasions or understood the depth and extent of this problem. Control of invading plants has proven to be difficult, expensive and often ineffectual (Warnock and Lewis, 1980). Land management agencies should emphasize prevention of invasion rather than control of established invaders (USDI-BLM, 1994).

OBJECTIVES

PRINCIPLES

Many ecologists have expressed concern about invading plant taxa because of their adverse environmental impacts (Soulé, 1990, Temple, 1990, Bazzaz, 1986, Vitousek, 1986). There is interest on the part of the public in these plants, as evidenced by the large number of popular books on weeds. There is a concern by some personnel in various agencies to focus attention on these important issues (USDI- BLM, 1994, Salwasser, 1989, Losensky, 1987).

Land management agencies have failed to address the causes of biological invasions of alien plants and develop effective prevention and control strategies. Plant invasions remain one of the most serious threats to the long-term maintenance of regional biodiversity (Johnson et. al., 1994, Clary and Medin, 1990). Severe costs-degradation or even destruction of biological resources-have resulted from policies of nonaction and inappropriate action (Cottam and Stewart, 1940). To be effective, policies need to be based on an understanding of the biology of invading species and must place higher priorities on prevention of new introductions and stopping the further spread of invaders (Campbell, 1993).

Terminology
This paper attempts to adhere to a consistent terminology (Bazzaz, 1986, Lincoln et. al., 1990). "Colonizing" species are those that have recently entered unoccupied habitats, while "invaders" are those colonizers that have gone on to displace native components or which have become dominant in parts of their new environment. "Noxious weeds" are used with reference to legally defined plant entities. "Alien" or "exotic" taxa refer to any species generally viewed as non- native, on non-indigenous to new parts of its present range, while "introduced" taxa will refer to those aliens disseminated by man.

Effect of Alien Plants on Ecosystems in the ICRB
Alien plants alter ecosystem function and composition in several ways:

The following examples illustrate how plant invasions have recently altered ecosystems in the Pacific Northwest: Causes of Plant Invasions in the ICRB
Plant invasions are largely caused by human activities which disturb native ecosystems (Sheley, 1994, USDI-BLM, 1994, Harrod, 1994). Vegetation removal and ground disturbing activities create opportunities for colonization by alien plants (Orians, 1986, Bazzaz, 1983). Transportation of alien plant propagules is often accomplished through deliberate or inadvertent human activities or the behavior of livestock (Guillerm 1991, Durgan, 1989). On public lands, the primary activities which promote the spread of alien plants are road building and road use, logging, grazing, forage seeding, and some erosion control and fire rehabilitation measures (Saunders et. al., 1991, Tyser and Worley, 1990, Wilcove, 1989, Le Houérou, 1987).

Consequences of Plant Invasions
Management activities associated with logging, roads, and grazing are rapidly accelerating the rate of plant invasions on public lands in the ICRB (Johnson et. al., 1994, Tyser and Worley, 1992, Scott et. al., 1988). Infestations of noxious weeds (only a small subset of alien taxa) are doubling every 5-6 years on BLM lands in the ICRB (USDI-BLM, 1994). A total of approximately 393 taxa have currently been identified as invaders within the North Cascades and Columbia Basin (Wooten and Morrison, in prep.) These alien plants have already lead to great resource damage resulting in considerable economic costs (USDI-BLM, 1994, O'Toole, 1988). Alien plant invasion have led to endangerment of native species and plant communities (Weaver et. al., 1989, Chicoine et. al., 1988, Tyser and Key, 1988). Numerous cases exist where environmental and legal thresholds for degradation and disturbance have been exceeded (Penders, 1995, Warnock and Lewis, 1980). Public agencies are unprepared to face coming land management challenges in this rapidly changing field. Prevention of further spread into unroaded, unmanaged and relatively pristine areas is critical to long-term conservation of ecosystem resources, as these areas still retain undisturbed native flora and natural resilience to management-induced disturbances (DeAngelis and Waterhouse, 1987, Johnson et. al., 1994, Hobbs and Huenneke, 1992, West, 1993, Wilson, 1989).

Environmental Effects of Weed Control with Herbicides
In 1989, a five year injunction against herbicide spraying by the Pacific Northwest Region Forest Service was lifted after preparation of the Final EIS and Accompanying Record of Decision on Managing Competing and Unwanted Vegetation (Torrence, 1988), and the associated mediated agreement between the USDA and plaintiffs Northwest Coalition for Alternatives to Pesticides (O'Brien, 1989), in which provisions for priority of prevention strategies and use of herbicides only as a last resort, were stipulated along with government requirements to perform site-specific analysis and monitoring.

The excessive reliance on chemical control measures commonly found in federal land management policies has no place in an integrated weed management strategy and sound ecosystem management. This emphasis also dominated the scientific contract report on noxious rangeland weeds for the Interior Columbia Basin Ecosystem Management Project (Sheley, 1994). This violates both the letter and intent of the mediated agreement in which herbicide use is to be used only as a last resort.

For years herbicides were widely used to control plant invasions. Adverse environmental and human health effects associated with herbicide application are becoming increasingly apparent (Feldman, 1991, Warnock and Lewis, 1980, Katan and Eshel, 1973, Pimental, 1982), as in the following examples:

Environmental Effects of Integrated Weed Management
Biological controls are insects or pathogens that control populations of undesirable species. Such pathogens may be natural components in the original habitat of a weed, that are absent in the new environment. After confirmation of specificity to target plants, biological controls have resulted in spectacular effects on target organisms (Piper, 1984, Kelleher, 1984), as exemplified by the following example. Tansy ragwort (Senecio jacobaea), a noxious weed affecting much of Oregon and Washington, has been reduced to about 10% of mid-1970 infestation rates by a biological control program. Benefits of the program, utilizing cinnabar moth, ragwort seedhead fly and ragwort flea beetle, approximate $5 million annually, a return on investment of 83%, a benefit-to-cost ratio of 13:1 (USDI-BLM, 1994).
RECOMMENDATIONS AND GUIDELINES

Program Development and Cooperative Agreements
Each agency or jurisdiction in charge of maintaining land-based resources needs to develop and maintain an alien plant program with funding and manpower responsible for the prevention and control of invading species. Individual programs should be designed to be compatible with ecosystem processes for the particular area, and be specific to the invading plants and characteristic causes of invasions for each area.

Cooperative agreements between private interests, non-governmental organizations, federal, state and local governments should be encouraged in countering the invasion of alien plants. Land managers, field personnel, ecologists, botanists and biologists should be consulted about the nature and spread of invading taxa, as well as invaded ecosystems. Public interest and environmental groups should be allowed a chance to contribute. These groups can give invaluable support and manpower in solutions to weed spread. Efforts should be made to contact and educate all groups whose activities may increase the spread of alien plants.

Information Gathering
Identification of the nature and extent of plant invasions in each jurisdiction should be conducted by combining a review of known occurrences with additional surveys for new invaders. Baseline monitoring data will allow subsequent surveys to determine population trends, causative factors, rate of spread, persistence and potential for further spread into adjacent ecosystems. Review and amend lists of invading taxa and policies for their prevention and control following analysis of this data.

Prevention Strategies
Prevention strategies should be stressed over control measures, as control measures are futile once a certain population threshold is attained in the invading species. Prevention should be based on prioritization of areas based on a combination of ecosystem values and the threat of invasion as follows:

Priority 1 are those areas with intact ecosystem processes, essentially free of invaders. No management activities should be allowed which cause deliberate or inadvertent introduction of alien plants. Management objectives should put maintenance of unpolluted flora as a top priority.

Priority 2 are intact ecosystems which possess only a few invading taxa. Invaders threaten the ecosystem, plant community structure or landscape-level processes, but control efforts may be successful. No management activities should be allowed which cause further introduction of alien plants. Management objectives should emphasize environmentally benign but aggressive biological and mechanical control measures to reduce or eliminate alien plant populations.

Priority 3 are intact native ecosystems which possess only a few invading taxa that do not appear to threaten the ecosystem, but the spread of which may still be worth controlling. No management activities should be allowed which cause further introduction of alien plants. Management objectives should emphasize environmentally benign biological and mechanical control measures to reduce or eliminate alien plant populations.

Integrated Weed Management
Strategies for control are both more complicated and more costly. Control is a treatment strategy-not a prevention strategy. In general, control measures should be undertaken based on a prioritization procedure combining nature, quantity and number of invading species, their potential for spread to adjacent ecosystems, the nature of affected ecosystems, loss of values because of their spread, and long-term costs of control. Strategies based on these attributes are documented in USDI-BLM (1994), Harrod (1994), USDA Forest Service (1990), Torrence (1988, and the associated mediated agreement) and Hoglund et. al. (1991). Control strategies come under agency guidelines for integrated weed management (IWM). IWM begins with information gathering, surveying, and determination of a damage threshold (Hoglund, 1991). For control measures, action strategies are then further developed that incorporate education, prevention, mitigation, and control alternatives (USDI-BLM, 1994). Environmentally benign mechanical and biological control methods should be used in almost all cases on public lands. Herbicide use should be considered as a last resort only after biological consultation to ensure no damage will occur to native flora and fauna and human health is not endangered. All other measures must be exhausted before herbicide use is contemplated.

Adaptive Management
Deleterious management practices that contribute to the spread of alien taxa should be reexamined and revised. These would include seeding invasive species, using contaminated seed mixes, feeding with contaminated grain, transporting of weeds on stock, gear and clothing, and avoidable disturbances to soil, water and nutrients. Some of these are ingrained practices that will require infrastructure changes of land management agencies.

Further plant invasions caused by vegetation removal and ground disturbance (e.g. roading, logging and grazing), can be prevented by restricting these activities from intact native ecosystems (e.g. roadless areas and wilderness), where the effects of man are still largely unfelt. These areas are the highest priority for prevention strategies, and retain the last vestiges of resiliency present in native ecosystems of the ICRB. There is little moral or ethical ground for degrading these last remnants of pristine landscape. In other areas where alien plants are already well established, there must be some acceptance that biological invasions are often irreversible.

Education
The need for management of invading plants requires a long-term commitment to education and awareness of the nature and extent of this problem. Plant and weed identification needs to be routine for land managers and should also be available to the public. Signs, brochures, posters and news articles offer a chance for communication about the problem. Workshops and classes are recommended that bring interested people together in informative, problem-solving formats.

Research
There is an overwhelming need for more data on the ecology and biology of plant invasions in the ICRB. Agencies and educational institutions need to invest in research and methods that have the potential for solving the problems of invading species. Through cooperative agreements, cost-sharing and data-sharing, a better understanding of plant invasions will produce more effective prevention strategies and control techniques. Affected ecosystem components need to be studied, and at-risk ecosystems such as riparian areas should receive high priority. Specific topics that deserve attention include nutrient cycling, mycorrhizal connections, effects on wildlife, effects on biodiversity, biological controls, cultural (ecological) controls, research on target-specific or non-toxic herbicides, mechanisms of spread, genetics and reproductive biology of invading species, and the effects of varying the nature, severity and kind of causative disturbances.

FEDERAL AND STATE LAW ADDRESSING PLANT INVADERS

Numerous federal laws, regulations and policies have been established that address management of plant invaders on public lands. Designated "noxious weeds" receive individual consideration through several of these policies. A recent USDI publication (US Department of the Interior, BLM, 1994, Appendix 2), lists those laws pertaining to the agency's role in their management, and includes brief interpretations of the intent of those laws:

REFERENCES